The LIFE initiative has the goal to develop the science, the technology and a roadmap for an aspiring space mission that will allow humankind to detect and characterize, via nulling interferometry, the atmospheres of hundreds of nearby extrasolar planets including dozens that may be similar to Earth. This follow-up talk will tackle more of the techniques and technologies that will enable such an ambitious undertaking. I will outline the underlying measuring principle, and provide some overview over essential technologies, their current status and necessary developments.

1. LIFE - the Large Interferometer for
Exoplanets (II) - Technology
Hendrik Linz
MPIA Heidelberg
LIFE Initiative
Technology that
enables the search
for extrasolar life in
our neighbourhood
in the next decades

2. 2
Who I am …
Hendrik Linz
MPIA Heidelberg & ETH Zürich
Astrophysicist
(high-mass star formation, circumstellar disks,
interferometry)
Instrument Control Center for Herschel/PACS
Feasibility study for a space interferometer (IRASSI)

3. Some Motivation … what was this LIFE thing
all about?
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4. ESA news
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ESA announcement regarding
Voyage 2050
contained language supporting the launch of
"A large mission enabling the characterisation
of the atmosphere of temperate exoplanets in
the mid-infrared"
and that it
"should be a top priority for ESA within the
Voyage 2050 timeframe".

5. Image credit: NASA/NOAA; NASA/NOAA GOES Project; NASA; LIFE Initiative/ETH Zurich
Reflected light (UV - NIR) Thermal emission (MIR)
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The LIFE initiative in an international context

6. Image credit: NASA/JPL Caltech
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Schwieterman et al. 2018

7. The Approach
Thermal infrared → appropriate detectors and optics that have
to operate over > 2 octaves (4-18 µm)
→ cryo measurement conditions
Stable low background → go outside Earth atmosphere (satellites!)
High spatial resolution → necessary values demand long baselines
(30 … 100s of meters)
→ interferometric solutions
→ formation flying
Best concept for weak offset detection → nulling interferometry
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8. Heritage
Space based (MIR,
nulling) interferometry
is not a new idea.
What is new is that we
now know Exoplanet
statistics much better,
thanks to Kepler, K2,
TESS, and CHEOPS.
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9. —————————————————————————————————-
Direct detection and characterization in thermal emission
Image credit: LIFE initiative
@LIFE_Telescope www.life-space-mission.com
4 collector
telescopes
1 beam combiner
spacecraft
1
2
3
4

10. Nulling in a nutshell
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11. 11
Nulling 101
Credit: D. Rouan
Bracewell interferometer (Nature 274:780, 1978)

12. 12
Nulling on the next level
Credit: F. Dannert
Bracewell interferometer (Nature 274:780, 1978)
4- Telescope setup
“Dual-chopped Bracewell”
→ There are constructive outputs
(1 and 2)
→ There are destructive outputs
(3 and 4)
In one branch, a p/2 phase shift
is introduced to enable the
difference map of Out3 and Out4

13. 13
Nulling on the next level
Difference map is antisymmetric wrt to central point → filters out point-symmetric emission → offset planet remains
Array rotation (on timescales of 16 – 20 h) will lead to a virtual path of the exoplanet emission through the difference map
Bracewell interferometer (Nature 274:780, 1978)
, id. 016001 (2020).
Credit: F. Dannert

14. 14
Nulling 101 Credit: F. Dannert
Up: The difference map
in polar coordinates
Down: Transmission path
of an offset planet
during a full
array rotation
Array

15. Launchers
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16. 16
Plans for DARWIN in the 2000s:
4 collector spacecraft + 1 beam
combiner unit (total weight 6-6.5 tons)
Launch planned :
→ either with one Ariane 5 ECA
→ or with two Soyuz/Fregat launchers
But in 20 years from now … neither will
be available anymore!
An Ariane 5 ECA, lifting JWST into space on
Dec 25, 2021

17. 17
Ariane 64 (Maiden flight for
Ariane 6 expected for 2022 …)
Seems promising to lift such a facility!
See numbers from 2021 manual:
Up to 8 tons into an L2 transfer orbit
Ad drawing of the Ariane 64
(Arianespace)

18. 18
Possible Alternative: SpaceX‘
Falcon Heavy
Even more powerful than the Ariane 64
(if rocket fully expandable)
Cheaper than the Ariane 64
(if central and side boosters reuseable)
→ Realistic price tag for 8 tons of
payload to an L2 transfer orbit might
not be so far off from the Ariane 64
→ standard fairing size of Falcon Heavy
somewhat smaller than for Ariane 64
Maiden flight of the Falcon Heavy in 2018
(SpaceX)

19. Formation Flying
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20. 20
LIFE as formation flying spacecraft facility
Two concepts from the DARWIN Assessment studies:
Left: co-planar array with Right: out-of-plane beam-
relay optics in the collectors combiner with siderostats

21. 21
Prisma (2010)
Small satellite mission under
leadership of Sweden
→ Test formation flying using GPS,
RF, and optical sensors
→ test several types of (micro-)
thrusters
→ position and velocity knowledge
via GPS: 10 cm and 1mm/s, resp.
(D‘Amico et al. 2012, JGCD 353, 834)
General sketch of the PRISMA satellites Mango & Tango

22. 22
Proba-3 (2023) – ESA
New benchmark for formation-flying
control
→ Test formation flying to mm and
arcsec precision
→ Operate and manoeuvre
autonomously w/o ground control
→ occultation experiments
→ cold-gas micro-thrusters for fine
manoeuvering
Artist impression of the Proba-3 spacecraft (© ESA)

23. 23
CubeSat missions for tests and demonstration
RACE – (European consortium + ESA’s
General Support & Technology Programme)
→ in-orbit testbed for advanced guidance,
navigation and control software and
autonomous system behaviour
launch in 2022-2023 (?)
Starling (NASA)
→ 4 cubesats at wider separation
→ Testing swarm dynamics and different
levels of autonomy
→ establishing a local communication network
launch mid of 2022 (?)

24. 24
A sidenote on metrology
Laser metrology via a method
„Dual Frequency Comb interferometry“
(Coddington et al. 2009)
Investigated in a German feasibility study
(2015 – 2019) for a free-flying far-infrared
interferometer (IRASSI)
Industry partner: Menlo Systems GmbH
Start with lab experiments for a proof of
concept
Within 1 ms cadence, an accuracy of 1 µm
can be achieved … ! Taken from Linz et al. 2020, Advances in Space Research 65, 831

25. 25
A sidenote on metrology
As a spin-off: miniaturisation to go from bulky lab racks to more realistic setups → higher TRL
Shown sketch and photo are from a test setup: TEXUS II experiment (2018) on a sounding rocket
(Pröbster et al. 2021, JOSA B 38, 932)
Possibility to have a frequency comb setup on the ISS (~2024)

26. Low-noise Detectors in the Mid-Infrared
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27. 27
Si:As BIB detector array for the MIRI instrument onboard
the JWST (from Roellig et al. 2020)
The detector scene 15 years ago:
Si:As semiconductors as proven
technology (but mainly US heritage)
→ has to be cooled to ~6 Kelvin
→ delivers low read-noise and low
dark current for application in the
mid-infrared (5-28 micron)
The situation today: one top player
in the industry (Raytheon) has
stopped producing such arrays
DRS still experimented with Si:Sb for
the MIR camera for SPICA … but
SPICA in its original form will not
come!
When all still was right in detector world …

28. 28
Looking for detector alternatives (I)
MCT detector array for the planned NASA
mission NEO Surveyor (from Roellig et al.
2020)
Exploring other promising semiconductor
materials: HgCdTe = MCT
→ well established for NIR applications (1-
2.5 µm)
→ in recent years: highly sensitive MCT
arrays for the range 1-5 µm
→ Today: experimental arrays sensitive out
to 15 (or even 17 µm), mostly from
Teledyne (US)

29. 29
Looking for detector alternatives (II)
Dark current (e-/s/px) vs detector temperature for an
experimental MCT device (Mario Cabrera, PhD thesis
Uni Rochester 2020)
Tuning these MCT devices for long-
wavelength applications is tricky!
Quantum mechanics effects
(sometimes, mitigating one of the effects
worsens an other effect)
In short: current performance regarding
dark current is at least a factor of 100
away form the desired level (<0.1 e-/s/px)
NB: European MCT detector development
triggered by ESA (TDE):
AIM (DE) & Sofradir (Fr): T217-055PA(-B)
Progress, but still very high dark currents
(Hanna+ 2016, 2020; Gravrand+ 2016)

30. 30
Looking for detector alternatives (III)
Inner workings of a KID for near-infrared use
(courtesy of Pieter de Visser, SRON)
Other measurement principles exist:
Transition-Edge Sensors (TES)
Kinetic Inductance Detectors (KIDs)
→ Not yet fully explored for MIR
applications
→ Advantage of KIDs:
Good multiplexing capabilities;
Devices are energy-resolving (R~50);
one can more clearly separate noise
from signal
→ Inconvenience: operation at << 1 K

31. Optical components and Lab Experiments
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New R&D efforts to demonstrate nulling under cryogenic conditions
Component development – in collaboration
… but also several members of the LIFE Initiative,
e.g., Prof. L. Labadie (Uni Cologne)
Differential Delay
Lines
(symbolically, the
VLTI lines are
shown!)
< 5 nm rms !

33. —————————————————————————————————-
New R&D efforts to demonstrate nulling under cryogenic conditions
Gheorghe et al. 2020
10 micron cryogenic nulling test bench (with planet simulator and realistic flux levels)

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New R&D efforts to demonstrate nulling under cryogenic conditions
Gheorghe et al. 2020
Warm precursor (4 micron, ambient conditions, incl. metrology system)

35. Take home message
LIFE is an ambitious project with ambitious goals:
Detection and Characterisation of Earth-like exoplanets
LIFE Approach : nulling interferometry in space in the thermal IR
Building on the previous studies DARWIN/TPFI, we follow up on
progress in key technologies, and stimulate new developments.
LIFE is a growing initiative that is eager to tackle the technical
challenges and to make LIFE as a project become reality.
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36. Check our webpage: www.life-space-mission.com
Sign up for mailing list: life@phys.ethz.ch
@LIFE_Telescope
lifespacemission.slack.com
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The LIFE initiative is not a closed club
Advisory Board

37. Thanks for your attention!
Questions, comments, …
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